1. Field of the Invention
The invention relates to the field of automatic test equipment for semiconductor devices, and more particularly to a precision measurement unit having clamps that limit voltage or current spikes to a device under test and that protects against inadvertent user reversal of the clamp range settings.
2. Description of Related Art
As part of the manufacturing process, semiconductor devices are subjected to various tests in order to identify faults. This testing can occur at multiple points in the manufacturing process, including testing done before packaging and testing done after packaging. Manufacturer testing of semiconductors is often performed using equipment referred to as automatic test equipment, or ATE. An ATE system can be used in a wide variety of applications, including the identification of defective semiconductors and the sampling of parts for quality control.
Automatic test equipment further includes specialized semiconductor devices known as precision measurement units, or PMUs, that are used to force a signal to a device under test (DUT) at a particular current or voltage, and/or to sense the voltage or current from the DUT in response to the forcing signal. An example of a per-pin PMU device is the Edge4707 part manufactured by Semtech Corporation. This device has four channels that can each be independently configured to force voltage or current to a DUT and to sense voltage or current from the DUT. ATE systems with a large number of individually controllable pins can be constructed using multiple PMUs and the PMUs can have multiple ranges of operation. In the case of the Edge4707, there are four current ranges available in the force current mode, with each being selectable using an input selection control and external resistors.
It is known to include clamps in the PMU device that limit the voltage or current spikes that might result from changing the current range or changing the operating mode of the PMU. For example, the high limit voltage (HLV) and low limit voltage (LLV) are limit ranges of the clamps that may be programmed by the user for a particular application. But, if the user inadvertently reverses the programming of the clamp HLV and LLV parameters, i.e., programming the HLV voltage or current spikes can pass to the DUT and/or PMU, which could thereby damage the parts. It would therefore be desirable to provide a PMU device having clamps that limit voltage or current spikes to a DUT and that protects against inadvertent reversal of the clamp range settings.